In the manufacture of integrated-circuit semiconductor devices, involving numerous operations including dopant-ion implantation, dielectric and metallic layer deposition, and photolithographic pattern definition and etching, it is desirable to produce etched openings or windows in dielectric layers having sloping or tapered profiles. Resulting openings may be intended for at least partial filling with a conductor material such as, e.g., aluminum, and sloping of profiles is largely in the interest of facilitating surface coverage by such material.
One method for making tapered openings, disclosed by M. P. Karnett, "Tapered Wet Etching of Contacts Using a Trilayer Silox Structure", SPIE, Vol. 772 (1987), pp. 166-171 involves etching of a three-layer structure deposited by chemical-vapor deposition, with a middle layer of phosphosilicate glass. Another familiar method uses twin etching steps, namely a step of wet etching so that a photoresist pattern is undercut, followed by a step of reactive-ion etching using the same photoresist pattern to further etch the dielectric straight through the remainder of its thickness.
One concern arising with methods involving wet etching of dielectric material arises with the tendency of photoresist material to separate from the dielectric in the course of etching, and the invention as described below is motivated by the desire for guarding against such tendency.